Zoran V. Saponjic

New Hybrid Properties of TiO2 Nanoparticles Surface Modified With Catecholate Type Ligands

Surface modification of nanocrystalline TiO2 particles (45 Å) with bidentate benzene derivatives (catechol, pyrogallol, and gallic acid) was found to alter optical properties of nanoparticles. The formation of the inner-sphere charge–transfer complexes results in a red shift of the semiconductor absorption compared to unmodified nanocrystallites. The binding structures were investigated by using FTIR spectroscopy. The investigated ligands have the optimal geometry for chelating surface Ti atoms, resulting in ring coordination complexes (catecholate type of binuclear bidentate binding–bridging) thus restoring in six-coordinated octahedral geometry of surface Ti atoms. From the Benesi–Hildebrand plot, the stability constants at pH 2 of the order 103 M−1 have been determined.

Synthesis and characterization of CdS quantum dots–polystyrene composite

Methodology for incorporation of 50 A CdS quantum dots (QD) in a polystyrene matrix, based on phase transfer of CdS quantum dots from an aqueous to organic phase, was developed. The obtained composite was characterized using optical, structural and thermal techniques. Infra red measurements revealed formation of chemical bonds between the surface of the CdS QDs and the polystyrene matrix. The polystyrene matrix blocked the surface states that promote radiationless recombination, resulting in enhanced band-to-band luminescence of CdS QDs. On the other hand, in the presence of CdS QDs the thermal decomposition of polystyrene was shifted towards higher temperature for about 100∞C. ” 2000 Elsevier Science B.V. All rights reserved.

Improved properties of oxygen and argon RF plasma-activated polyester fabrics loaded with TiO2 nanoparticles.

The potentials of low-pressure capacitively coupled RF oxygen and argon plasmas for the activation of polyester fibers surface that can enhance the deposition of colloidal TiO(2) nanoparticles were discussed. SEM and XPS analysis confirmed the plasma-induced morphological and chemical changes on the surface of polyester fibers. Oxygen and argon plasma pretreated polyester fabrics loaded with TiO(2) nanoparticles provided maximum reduction of Gram-negative bacteria E. coli and UV blocking. The self-cleaning effects tested on blueberry juice stains and photodegradation of methylene blue in aqueous solution proved excellent photocatalytic activity of TiO(2) nanoparticles deposited onto fiber surface. Although both plasmas significantly contributed to overall improvement of properties of such nanocomposite textile material, oxygen plasma treatment, in particular, enhanced the deposition of colloidal TiO(2) nanoparticles and thus ensured superior effects.

Plasma-induced Decolorization of Indigo-dyed Denim Fabrics Related to Mechanical Properties and Fiber Surface Morphology

The aim of this study was to investigate how morphology of fibers is affected by plasma during the process of decolorization by a low-pressure RF plasma (gas, treatment time, and power were varied) and atmospheric pressure industrial corona (number of passages and power). CIE LAB colorimetric system was used for determination of color difference between untreated and differently plasma-treated denim fabrics. Particular emphasis was put on the morphological changes induced by plasma treatment, because they indicate changes in mechanical properties of the fabrics. The morphology of plasma-treated fibers was analyzed by scanning electron microscopy (SEM). SEM images revealed that, when plasma conditions that lead to a decolorization were chosen, specific fiber surface changes were always observed in the form of submicrometer-sized striations, pits, and cracks. Mechanical properties of denim fabrics were moderately influenced by treatment conditions. The results indicated that decolorization was highly affected by plasma parameters and desired `worn look effects could be designed by adequate control of plasma processing while paying attention to limiting the plasma-induced damage.

Charge-transfer reactions of C60 in surfactant-based complex fluid media

Abstract Surfactant-based complex fluid media enables the investigation of charge-transfer reactions between a hydrophobic C 60 molecule and hydrophilic solutes. The formation of a ground state charge-transfer complex between C 60 and ethylamine was demonstrated in an ionic surfactant/water/oil microemulsion, the value of the complexation of K = 1.1 M −1 was determined. The one-electron reduction of fullerene occurs in reaction with the excess electrons stored on nanometer-sized metal(Ag) or quantized semiconductor (TiO 2 ) particles in microemulsions.

Hybrid TiO 2 nanoparticles: an approach for developing site specific DNA cleavage

We have developed hybrid light responsive TiO2 nanoparticles electronically linked to PNA oligonucleotides that site specifically bind to double stranded target DNA. This opens a new opportunity for the development of a highly efficient artificial restriction enzyme whose activity can be controlled by using light. The work focuses on the use of TiO2 nanocomposites as analogs of restriction enzymes with unique specificity that does not exist in current biological approaches. TiO2 nanoparticles electronically linked to DNA or PNA adapters have been site-specifically attached along double stranded λ DNA vectors. Illumination of this assembly results in selective oxidation of DNA at the deepest thermodynamic traps located closest to the nanoparticle surface, causing DNA cleavage. We investigate the effect of the sequence and length of DNA and PNA adapters on the specificity of DNA cleavage. Related to this issue, the potential use of TiO2/DNA nanocomposites as rare cutters that cleave DNA in the places not achieved with existing protein-based enzymes is investigated.

Conductive biomolecules and their THz vibrational interactions: key aspects of bioelectronics

This paper focuses on understanding the THz-phonon mediated transport of polarons in biomolecules, with particular attention on polaron transport in DNA. In order to exploit biology-based approaches to realizing new electronic systems, it is necessary to understand the electrical transport properties and THz-phonon interactions of biomolecules that portend applications both as electrically conductive wires and as structures that facilitate the chemically-directed assembly of massively integrated ensembles of nanoscale semiconducting elements into terascale integrated networks. Special attention is given to charge transport in biomolecules using indirect-bandgap colloidal nanocrystals linked with biomolecules.

Synthesis and Characterization of Electrospun Poly(vinyl pyrrolidone) (PVP) and Poly(vinyl alcohol) (PVA) Nanofibers with Au Nanoparticles

S. Mishra,* S. P. Ahrenkiel,* V. V. Vodnik,** Z. V. Saponjic,** and J. M. Nedeljkovic** * Nanoscience and Nanoengineering Ph.D. Program, South Dakota School of Mines and Technology, Rapid City, SD 57701, USA ** Vinca Institute of Nuclear Sciences, P.O. Box 522, 11001 Belgrade, Serbia Electrospinning is an electrical, jet-based method of fabricating nanofibers that involves the application of a very high electrostatic force on the capillary containing the polymer solution or polymer-melt. The fibers are created by an electrically charged jet of the polymer solution, which can be collected on the surface of a grounded template. The incorporation of metal nanoparticles produces functional nanofibers. Among the noble metal nanoparticles, gold nanoparticles are promising because they have electronic, magnetic, optical and catalytic properties [1]. The solution for electrospinning poly(vinyl pyrrolidone) (PVP) nanofibers was prepared by mixing varying concentrations of 10 nm Au nanoparticles-colloidal solution and PVP (average M.W. 1,300,000) in isopropyl alcohol (IPA). The electrospinning was carried out at 15 kV to produce non-woven mats of fibers with diameters ranging from 85 nm to 1 µm. Using a Hitachi H-7000 FA TEM, we could confirm the presence of Au nanoparticles within the amorphous PVP matrix (Fig. 1A and 1B). The distribution of Au nanoparticles in the PVP fibers was completely random. Au/PVA nanocomposite films were prepared by using colloidal solution of Au nanoparticles and poly(vinyl alcohol) (PVA) (average M.W. 72,000) as precursors. A colloidal solution of 0.91 mM Au was prepared [2]. Direct mixing of 1 ml of 5 mass% aqueous PVA solution with 12 ml of 0.91 mM Au colloidal solution lead to formation of stable transparent PVA/Au dispersion. The mixture was placed in a Petri dish and dried in air. After solvent evaporation, a transparent, 4.1 wt% Au/PVA film was obtained. PVA nanofibers with Au nanoparticles were prepared by electrospinning a solution made by dissolving the PVA thin films containing Au nanoparticles, with average diameters ranging from 15 nm to 30 nm, in H

ENVIRONMENTAL EFFECTS INFLUENCING THE VIBRATIONAL MODES OF DNA: NANOSTRUCTURES COUPLED TO BIOMOLECULES

The interactions of charges in DNA with the vibrational modes in DNA depend on the spectra of these vibrational modes. Using (a) the Su-Schrieffer-Heeger (SSH) Hamiltonian approach, (b) integrated structures of DNA and manmade nanostructures, and (c) gel electrophoresis techniques,1 the interaction between charges in DNA and the vibrational modes of DNA are investigated. As is well-known, DNA has a rich spectrum of modes in the THz spectral regime. The use of manmade nanostructures integrated with DNA facilitates the engineering of nanoscale systems useful in studying the role of environmental effects on the vibrational modes of DNA as well as the interaction of these modes with charge carriers in DNA. Among the DNA-based structures considered in this account are: B-DNA and Z-DNA strands related by a conformational change; and DNA molecules bound on one terminal to indirect bandgap semiconductor quantum dots. Gel electrophoresis is used as a tool for the analysis of carrier interactions in novel integrated DNA-manmade-nanostructure complexes, and models based on the SSH Hamiltonian2 are employed as a means of analyzing the interactions between the vibrational modes of DNA and charge carriers in DNA.3-4

INTERACTIONS OF THz VIBRATIONAL MODES WITH CHARGE CARRIERS IN DNA: POLARON-PHONON INTERACTIONS

This paper presents models and experimental measurements that shed light on THz-phonon mediated transport of polarons in biomolecules. Polaron transport in DNA has been considered recently in view of the expected derealization of charge carriers on a one-dimensional wire as well as the highly charged nature of DNA.1,2 An understanding of the electrical transport properties and THz-phonon interactions of biomolecules is important in view of DNAs potential applications both as electrically conductive wires and as structures that facilitate the chemically-directed assembly of massively integrated ensembles of nanoscale semiconducting elements into terascale integrated networks. Moreover, understanding these interactions provides information of the THz spectrum of vibrational modes in DNA. A primary focus of this paper is on charge transport in biomolecules using indirect-bandgap colloidal nanocrystals linked with biomolecules.3 Through a combination of theoretical and experimental approaches,4-7 this paper focuses on understanding the electrical properties and THz-frequency interactions of DNA. Moreover, this paper presents observed charge transport phenomena in DNA and discusses how these measurements are related to carrier scattering from the THz vibrational modes in DNA. Indeed, carrier transport in DNA is analyzed in light of theoretical calculations of the effects of THz-frequency phonon emission by propagating carriers, THz-frequency phonon absorption by propagating and trapped carriers, and effective mass calculations for specific sequences of the DNA bases.1-7 These studies focus on THz-phonon-mediated processes since an extra carrier on a one-dimensional chain minimizes its energy by forming an extended polaron, and since many biomolecules, including DNA, exhibit THz vibrational spectra.8 Accordingly, these calculations focus on THz-phonon-mediated processes. These results are discussed in terms of the role of THz-phonon-mediated charge trapping and detrapping effects near guanine-rich regions of the DNA as well as on the understanding and identification of DNA with specific base sequences that promote charge transport. As in previous studies, optical excitation is used to inject carriers into DNA wires. Moreover, this paper reports on the use of gel electrophoresis to study charge-induced cleavage of DNA and the related transport of charge in DNA. Phonon absorption and emission from polarons in DNA,9 is analyzed using parameters from the well-known Su-Schrieffer-Heeger Hamiltonian.